PG&E is seeking approval from state regulators for a power purchase agreement with Solaren Corp., a Southern California company that has contracted to deliver 200 megawatts of clean, renewable power over a 15 year period.

Solaren says it plans to generate the power using solar panels in earth orbit, then convert it to radio frequency energy for transmission to a receiving station in Fresno County. From there, the energy will be converted to electricity and fed into PG&E's power grid.

I haven't found anything that explains how the power transfer works, anyone know? Is it an orbital death ray that heats a boiler on the ground, or what?

The wikipedia article suggests that the microwave beam will have about 25% of the areal power density of solar irradiation and run at about 85% conversion efficiency on the ground, for a total yield of about 21% of the solar irradiation constant for any given area. Presumably there's also some inefficiency in the solar-to-RF conversion in the satellite as well; let's call it 90% efficiency out of total ignorance.

Photovoltaics according to wikipedia are running in the 12-18% efficiency range, with much better yields now in the lab and presumably coming to market before long. Say we can get 21% efficient solar panels in the time it takes to get space-based solar working.

Discounting, just for a moment, the atmospheric losses, let's say the solar constant is 100 watts per unit area. One unit of orbital PV collects 21 watts of that, converts it to 19 watts of RF, beams it down to 0.75 area units of RF collector antenna, which converts it to 16 watts of electricity.

Or we build 1 area unit of ground based PV and collect 21 watts of electricity reduced by some atmospheric factor, and only working during daylight hours. But no launch costs. No additional crap crowding valuable geosynchronous orbits. And you can go out and fix the panels without a space suit. And add panels incrementally.

Let's say we want 2GW coming out of the ground station, enough power to match the Hoover Dam. If I've done the math right, we need something like a 3km x 3km square PV and a 200m circular radio antenna on the satellite.

Solaren's proposal is 1/10 of that power, so 1/10 of that area, call it 1km square PV and a 60-meter antenna. Do we have the slightest idea how to launch that?

Is someone at Solaren going to make a fuckton of money before anyone realizes that the promised power is not going to be delivered?

"The solar constant is the amount of incoming solar electromagnetic radiation per unit area, measured on the outer surface of Earth's atmosphere in a plane perpendicular to the rays.[2] The solar constant includes all types of solar radiation, not just the visible light. It is measured by satellite to be roughly 1,366 watts per square meter (W/mÂ²),"

Or we build 1 area unit of ground based PV and collect 21 watts of electricity reduced by some atmospheric factor, and only working during daylight hours

And only on sunny days. The problem with a lot of these green power schemes is that they're not dependable enough for baseline power, so unless you have some massive storage mechanism they can't be more than 10% or so of the grid regardless.

That's probably an argument for ground-based solar thermal, though, not space PV, which might make sense for military bases in Afghanistan, but not for much else at the time being...

I have an article on "space solar" from a class I was in. I'll find it for you.

This kind of big solar is a mixed bag. It's partly a way to get big companies in control of what could be a far more decentralized power source. However, I'm definitely of the "whatever it takes to get solar in" camp. I just wish we could stick to the simple solar heat powered steam turbines, or even PV cells (which are getting more efficient all the time). Why do we have to make things more complicated and difficult all the time?

It's not about the complexity, it's about how to generate enough power from solar collection to effectively supply our power-crazed civilization.

Consider, for example, that even if ethanol were an efficient means of creating power it would remain an impractical substitute for fossil fuels because of the sheer scale of the necessary production. The idea of a solar array atop each house and building is noble, but still would pale in comparison to the amount of energy consumed daily. Only part of the sun's energy reaches the surface of the planet, you can only generate power during the day, and when it's not cloudy, and so on.

And then you look at the area outside the atmosphere and think, Great Scott, it's a vast ocean of space positively drenched with raw, unfiltered solar power that we could scoop up in massive amounts and pipe down to the surface! Sure it's complex but that complexity is reducable, and it's something that could feasibly compete with fossil fuels for sheer mass of power output.

That's part of the problem. There are a lot of very practical folks out there like Arthur Rosenfeld and Amory Lovins who have advocated for energy efficiency for decades now and have been largely ignored. Energy efficiency is cost-effective and practical, and would greatly lower the need for sources of power such as space solar that require resources we can't really spare right now and time we don't have. Energy efficiency doesn't even require using less energy! It just requires using it better- using waste water from certain parts of a factory to fuel other parts, etc, and that's not even going into conservation, though after the Carter administration we know how unpopular that is!!!

We have to look at the problem (over-use and inefficient use of resources) before creating a "solution". Photovoltaics on each house is not a complete solution, but it can be part of a solution that includes more efficiency, large scale CSP, wind turbines, so on and so forth.

Anyway, I repeat...anything that can compete with fossil fuels (and nuclear!) is better than nothing!

You and I agree that energy efficiency is a better and more effective approach than creating massive amounts of energy. It isn't exactly popular, especially at the scale that is really necessary. It's also not directly profitable – nobody derives revenue from using less energy.

Also, remember that energy efficiency actually does require significant investment of resources. Perfectly functional items will have to be replaced with entirely new, sometimes extremely expensive models. Technologies that contribute to energy efficiency and carbon reduction can also have the side effect of contributing to pollution: fuel cells are currently in a form that are short-lived and not exactly environmentally friendly to dispose of.

All in all, I suspect that it's going to take a combination of new, more benevolent sources of power together with higher efficiency. And I figure that space-collected solar is one of the few things that can make a truly significant impact in clean power.

Also, efficiency isn't free. I said it is cost-effective. Since we are clearly in the era of cost-benefit analysis, we should use that here...and we should do it long-term as well as looking at what we can afford now. Energy efficiency, like small-scale solar, is most likely more profitable for small business, who I would rather support than PG & E.

Anyway, these are the kind of disagreements that I wish policy-makers would have in the public so that as a society we could look at the implications of different types of power. There are, as we seem to agree, lots of options.

Regarding solar, the author points out that the UK alone would take an area "the size of Wales" in the desert (Iberian or Saharan), and constructing some 20GW of transmission capability across the channel; he later sketches out the related figures for the USA (basically, cover Arizona with concentrating solar [thermal salts -> electricity, not PV]).

Or the heck with efficiency improvements, just make PV cheaper. It's just barely becoming affordable to put on a house, but only because of tax breaks. If you want to see serious change, make it cost-comparable to other forms of electricity. Then we'll see some real change happen...

To say nothing of that nagging problem of where to stick the icky radioactive waste. In keeping with our host's Grim Meathook Future bent, I'm guessing that Africa takes global climate change right on the chin, the population crashes and the sub-Saharan nations generally collapse, leaving vast swathes of the continent to become a nuclear dumping ground.

You can have the downward beam collimator isolated from the station's power supply and only able to draw power from a coaxial receiver powered by a beam coming up from the ground. This way if you lose alignment, the downward beam diffuses over an area too wide to cook.

Not in the game, you can't. I find it amusing that a throwaway comment about how a nuclear meltdown in SimCity 2000 only irridiates a few city blocks appears to have been taken as a serious criticism that this real-life project will turn the receiver station into a second Chernobyl.

Unless we can build some sort of exotic launch vehicle (maddest idea so far: the launch loop; my favourite is the Aerovator) I don't see space solar being cheap enough to be worth it. Even with it, the solar panels themselves are so expensive (compared to ground-based CSP)

For the cost of building solar power satellites we get a fleet that can be used to build other things in orbit. If they're reusable craft, that's great. If they're not we've still got the facilities and the engineers that built them, all handy.

In private hands.

We'd also have hundreds of citizens skilled in the art of building large structures in micro-gravity. Nobody has this right now, outside the government.

Well, somebody has to build a space-faring civilization. Damn sure the government isn't up for the job.